Method of improving flow properties of asphalt



Patented Dec. 25 1195 1 METHOD OF IMPROVING FLOW PROPERTIES OF ASPHALT Charles Mack, Sarnia, Ontario, Canada, assignor to Standard Oil Development Company,- a corporation of Delaware 1 No Drawing.

1 Claim.

The object of this invention is a method of improving the flow properties of paving asphalts. In accordance with this invention, paving asphalts of improved characteristics are obtained by incorporating small amounts of alphanitro-naphthalene in the asphalt.

In preparing a suitable bituminous composition for use as a paving asphalt, it is necessary that the composition obtained have several stringent qualifications. It is, of course, essential that good bonding of the aggregate be obtained and that the bond should be resistant to stripping, especially as aggravated by the presence of moisture. A further qualification of such asphalts is that they have desired now properties. In this connection if an asphalt pavement were rigid and subjected to a decrease in temperature amounting to 30 F. between the surface and the bottom, the internal stress at the bottom of the pavement would be of the order of 300 lbs. per square inch, and the pavement would crack. In order to prevent cracking, the internal stresses must relax. Since the mineral aggregate contained in the paving composition is unyieldi stress relaxation must occur through now of the asphalt. It is therefore the principal object of this invention to provide an asphalt paving composition having the desirable 'fiow characteristics. v

At the present time, many methods have been developed for suitably improving the bonding and stripping characteristics of asphalt compositions; for example, the patent issued to Hans Dohse and Fritz Spoun; U. S. Patent No. 2,191,295, discloses a wide variety of asphalt addition agents capable of improving the bonding and stripping characteristics of the asphalt. The teachings of this patent and of other literature in the art adequately prescribe asphalt compositions having suitable bonding and coating characteristics. However, it is an object of this invention to improve the type of asphalt compositions known to the art by employing an additional additive for utilization with known asphalt compositions whereby the flow properties of the asphalt compositions may be improved. It is to be understood, therefore, that the teachings of this invention may be employed with any bituminous composition in order to alter the fiow properties of the particular composition in the manner to be described.

It can be logically deduced that the stresses set up in a series of asphalts of the same viscosities and varying flow properties, relax at the greatest rate in asphalts of Newtonian or viscous flow properties (cf. C. Mack, Plastic flow, creep and stress relaxation, Pt. I-III, Journal of Applied Physics, vol. 17, pp. 1086-1107, 1946). This has also been verified experimentally (cf.=C. Mack, Rheology of bituminous mixtures relative mately 10 to 20% of asphaltenes by weight. As-

Application December 2, 1948, Serial No. 63,189

to the properties of asphalts, Proceedings of the Association of Asphalt Paving Technologists, vol. 13, pp. 194-255, 1942). It is, therefore, a more specific object of this invention to provide means of asphaltenes present in the asphalt. It is generally known that asphalts contain approxiphaltenes are of such a character that they tend to agglomerate into larger particles, particularly at decreasing temperatures so as to adversely af fect the flow properties of the asphalt. According to this invention, it has been discovered that the agglomeration of asphaltenes, or in any case the flow properties of the asphalt, may be favorably controlled by the addition of small amounts of aromatic amino compounds or aromatic nitro compounds. It is broadly believed that suitable compounds for controlling the fiow properties of asphalts are aromatic compounds having a strong polar group on the aromatic nucleus. In particular, it has been found that aromatic amines having 1-3 condensed" rings andhaving 1-4 amino groups suitably control the fiow properties of bituminous compositions. Similarly, it has been found that aromatic compounds having 1-3 condensed rings and having 1-4 nitro groups are efiective. The particular choice of a compound from the class indicated is limited only by the volatility of the compound; thus it is essential that the particular compound should not boil below about 500 F. as a lower volatility would cause the compound to be lost from the asphalt composition.

The nature and objectives of this invention will be clarified by consideration of the following examples showing the effective alteration in flow properties of asphalts obtainable by the practice ofthis invention. In each of these examples, the asphalts were subjected to two tests. The

first was a test generally identified as the ring and ball test and more specificallyas ASTM test 1136-26. This test is effective in indicating the softening point of the asphalt composition in T. The second test to which the asphalt compositions were subjected was a penetration test as prescribed by ASTM test 115-25 conducted at 77 F. and employing a gram force for successive periods of 5 seconds. These tests were sufficient to indicate the flow properties of the asphalt compositions by evaluation of the formula:

' C.=d log penetration/ d log t (of. C. Mack, Rheology of bituminous mixtures, Proceedings of the Association of Asphalt Paving Technologists, volume 13, pp. 194-225, 1942).

In the case of compositions obeying the principles of Newtonian flow, the constant C derived from the above formula is 0.5. In the case of plastic flow, this value of C is smaller than 0.5. In the case of sheer hardening and thixotropy, this value of C can be greater than 0.5. Therefore, the value of C was determined according to the indicated formula for each of the asphalt compositions tested. In considering the data obtained, it must be recalled that, as presented, it is valuble to obtain an asphalt composition having flow properties which approach the properties of a Newtonian liquid as closely as possible. In other words, it is desirable that the constant C obtained according to the formula given should be as nearly as possible 0.5.

EXAMPLE 1 A cracking coil tar was subjected to the ring and ball test, establishing that the softening point of this tar was 110 F. This same tar was found to have penetration at 77 F. of 108. The constant C for the cracking coil tar was therefore found to be 0.52. It may be noted that in this determination, as in other examples to be given, the value for the constant C was established correct to two decimal places.

EXAMPLE 2 The cracking coil tar having the properties indicated in Example 1, was subjected to the same tests after 1% of ortho-dinitro-benzene had been added to the tar. The softening point of this composition was 108, the penetration was 122, and the constant C was 0.50.

EXAMPLE 3 1% of alpha-nitro-naphthalene was incorporated in the cracking coil tar identified in Example 1 and was found to have a softening point of 108, a penetration of 134, and a constant C of 0.50.

EXAMPLE 4 The cracking coil tar of Example 1 was mixed with 1% of para-amino-diphenyl, with the result that a softening point was obtained of 109, a penetration of 128, and a constant C of 0.50.

EXAMPLE 5 1% of diphenylamine was added to the cracking coil tar of Example 1. This composition was found to have a softening point of 108, a penetration of 132, and a constant C of 0.50.

EXAMPLE 6 The cracking coil tar of Example 1 was subjected to the indicated tests together with 1% of para-benzylaminophenol resulting in asoftening point of 110, a peentration of 110, and a constant C of 0.50.

It will be noted from each of the above examples that a cracking coil tar not having Newtonian flow properties but actually having thixotropic properties was rendered Newtonian in properties by the addition of each of the additives identified. Further tests were also conducted employing an oxidized Mid-Continent asphalt. These tests indicated that this asphalt had a constant C when no additives were employed, of 0.38, a softening point of 129, and a penetration of 52. When 1% of ortho-dinitrobenzene, alpha-nitro-naphthalene, para-aminodiphenyl, or diphenylamine, were added to the oxidized Mid-Continent asphalt, the constant C obtained was 0.42. Similarly, when 1% of parabenzylaminophenol was incorporated in the asphalt a constant C was obtained of 0.40. It will, therefore, be observed that in these cases, as well as in the examples specifically given, as indicated by the values of C obtained, the asphalt was caused to have flow properties more closely approximating those of a Newtonian liquid.

Further experiments were conducted to determine the optimum quantity of additive to employ. These tests indicated that within the range of proportions tested, the amount of additive utilized is not critical. Thus it was found that from 15% ofo-dinitrobenzene and from 1-5% alphanitronaphthalene had substantially the same effect when incorporated in an asphalt. The results of these tests are indicated in the table.

Table BLENDS 0F CRACKING COIL TAB. AND O-DINITRO- BENZENE Penetration Per cent of o-dinitro-benzene 'Q m 77 F. grs. G

5 secs.

BLENDS 0F CRACKING COIL TAB AND ALPHA- It will be noted from this table that the asphalt employed, consisting of a cracking coil tar, initially was thixotropic in character as indicated by the constant C of 0.53. However, when 1%, 2%, 3% or 5% of either O-dinitro-benzene or alpha-nitronaphthalene were incorporated in the asphalt, the resulting compositions were each found to have Newtonian flow properties as indicated by the constants C of 0.50.

As described, therefore,in accordance with this invention, about 0.5-5% of a ar t pound containing nitro or amino groups are add-1 ed to an asphalt in order to improve the flow properties of the asphalt. As brought out, it is contemplated that the addition compounds of this invention may be utilized with any conventional asphalt compositions.

Having now fully described the invention, what is claimed is:

The method of improving the flow properties of an asphalt not having Newtonian fiow properties which consists of mixing in said asphalt from 0.5 to 5% of alpha-nitro-naphthalene.

CHARLES MACK.

REFERENCES CITED The following references are of record in the -file of this patent:

UNITED STATES PATENTS Number Name Date 2,085,992 Nelson July 6, 1937 2,396,669 .Auer -s -11-..- Mar. 19, 1946 2,465,960 .Den Berge 1-1-..- Mar. 29, 1949 2,500,208 Shea et a1. Mar.14,'1-950 

